#30719: Unable to use OuterRef(Expression(...))
-------------------------------------+-------------------------------------
Reporter: Matthew | Owner: nobody
Schinckel |
Type: New | Status: new
feature |
Component: Database | Version: master
layer (models, ORM) | Keywords: Subquery, OuterRef,
Severity: Normal | Expression
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 1
UI/UX: 0 |
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Whilst refactoring some code today, I noticed I had the following code in
a queryset method:
{{{
staff = Person.objects.filter(
first_name__iexact=OuterRef('_first_name'),
...
)
return self.annotate(
_first_name=Func(F('data'), Value('FirstName'),
function='JSONB_EXTRACT_PATH_TEXT', output_field=models.TextField()
).annotate(
candidates=Array(staff.values('pk'))
)
}}}
It's an annoyance to have to annotate on the expression to the outer
queryset, and then reference it in the inner queryset. It's also forcing
the database to do more work, because the SQL that is generated will
result in the expression being evaluated multiple times.
Instead, it will be much nicer to write:
{{{
staff = Person.objects.filter(
first_name__iexact=OuterRef(
Func(OuterRef('data'), Value('FirstName'),
function='JSONB_EXTRACT_PATH_TEXT', output_field=models.TextField()
)
)
return self.annotate(candidates=Array(staff.values('pk')))
}}}
(Note the second use of OuterRef there because we are referring to the
`data` from the outer queryset).
I believe the only change that is required to enable this is in
OuterRef.resolve_expression (and I have a working prototype on my 1.11
codebase).
Does this seem like a sane change to the functionality?
--
Ticket URL: <https://code.djangoproject.com/ticket/30719>
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